Compact multimodality optical coherence tomography imaging systems having a ring of optical fibers in image capture path

ABSTRACT

Systems for imaging a sample are provided. The system includes an optical coherence tomography (OCT) imaging portion having an associated OCT path defined by one set of optical elements between an OCT signal delivery optical fiber and the sample; an image capture portion having an associated image capture path defined by a second set of optical elements between an image capture device and the sample, different from the OCT path; and an illuminator portion having an associated illumination path defined by a third set of optical elements between an illumination source and the sample. The OCT path, the image capture path, and the illuminator path have at least one optical element in common, and the respective paths differ from each other by at least one optical element. The OCT path and the image capture path share a common intermediate conjugate image plane. Focal control is achieved for the OCT path and the image capture path concurrently through adjustment of one or more common optical elements distal to the common intermediate conjugate plane, such that focal control requires no differential adjustment between optical elements not in common to both paths.

CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.13/198,117, filed Aug. 4, 2011, which application claims priority fromU.S. Provisional Application No. 61/370,993, filed Aug. 5, 2010 and U.S.Provisional Application No. 61/412,558, filed Nov. 11, 2010, thedisclosures of which are hereby incorporated herein by reference as ifset forth in their entirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under grant number1R43EY01900 awarded by National Institutes of Health, National EyeInstitute. The United States Government has certain rights in thisinvention.

FIELD

The present invention relates to imaging and, more particularly, tooptical coherence tomography (OCT) and related systems and methods.

BACKGROUND

Visual field testing is a conventional clinical method utilized in thediagnosis of eye diseases that cause degradation of vision sensitivity.One method utilized in the diagnosis of such diseases is the StandardAutomated Perimeter (SAP) test, which tests brightness contrastsensitivity over a large visual field. There are many instruments forperforming an SAP test routinely used in clinics including, for example,those produced by Carl Zeiss Meditec (Dublin, Calif.).

Typically, visual field testing utilizes functional field testingtechniques. However, a functional field test technique is a functionaltest of vision degradation. Due to the human eye's complex multiplexingcapability, the functional field test is not a sensitive measure of eyestructure, which would be highly useful in the early diagnoses of sucheye diseases before substantial degradation has occurred. Suchstructural tests include, for example, retinal image testing and opticalcoherence tomography (OCT).

Retinal image testing can be performed with conventional optical imagingmethodology and has been routinely used in clinics for retinal structurechange evaluation in addition to visual field tests. Devices such as afundus camera, a scanning laser ophthalmoscope (SLO) or an indirectophthalmoscope are routinely used for such testing. The retinal imageprovides valuable information that clinicians can utilize to diagnosiseye diseases. However, only qualitative interpretation of eye structurechanges from the retinal photographs can be observed by highlyexperienced clinicians.

Accordingly, OCT has been used for non-invasive human eye retinalimaging. The cross sectional retinal image provided by an OCT system mayallow a clinician to quantitatively evaluate the retinal nerve layer andretinal thickness. Thus, the OCT system may provide valuable clinicalinformation that can be used for early diagnosis of eye diseases, suchas Age-Related Macular Degeneration, Diabetic Retinopathy and Glaucoma.

OCT has been adopted as a standard of care for structural imaging of theeye for retinal and anterior structures. Video fundus photography andscanning laser ophthalmoscopy remain important modalities for capturinghigh resolution, high contrast en face photographs. Additionally, thesemodalities are useful for color photography and fluorescent imaging thatprovide complementary signatures of disease.

To date, OCT imaging systems have been largely bulky tabletop systemsappropriate to clinical imaging of ambulatory patients. Handheld OCTproduced by Bioptigen is the first compact system for ophthalmic imagingof pediatric, confined, or infirm patients that does not require thepatient to sit a tabletop instrument as discussed in commonly assignedUnited States Patent Publication No. 2009/0268020.

The details of OCT systems used for imaging the human eye are discussedin, for example, U.S. Pat. No. 7,140,730 to Jay Wei et al. entitledOptical Apparatus and Method for Comprehensive Eye Diagnosis, thedisclosure of which is hereby incorporated herein by reference as if setforth in its entirety. OCT scanners used for imaging the human eye arediscussed, for example, in U.S. Pat. No. 6,741,359 to Jay Wei et al.entitled Optical Coherence Tomography Optical Scanner, the disclosure ofwhich is hereby incorporated herein by reference as if set forth in itsentirety.

Further discussion of OCT and related systems, methods and computerprogram product can be found in commonly assigned U.S. Pat. No.7,830,525 and United States Patent Publication Nos. 2007/0081166;2010/0315592; 2010/0321636; 2009/0141237 and 2009/0268161, thedisclosures of which are hereby incorporated herein by reference as ifset forth in their entirety.

SUMMARY

Some embodiments of the present inventive concept provide systems forimaging a sample. The system includes an optical coherence tomography(OCT) imaging portion having an associated OCT path defined by one setof optical elements between an OCT signal delivery optical fiber and thesample; an image capture portion having an associated image capture pathdefined by a second set of optical elements between an image capturedevice and the sample, different from the OCT path; and an illuminatorportion having an associated illumination path defined by a third set ofoptical elements between an illumination source and the sample. The OCTpath, the image capture path, and the illuminator path have at least oneoptical element in common, and the respective paths differ from eachother by at least one optical element. The OCT path and the imagecapture path share a common intermediate conjugate image plane. Focalcontrol is achieved for the OCT path and the image capture pathconcurrently through adjustment of one or more common optical elementsdistal to the common intermediate conjugate plane, such that focalcontrol requires no differential adjustment between optical elements notin common to both paths.

In further embodiments, the illuminator may include a compact wide fieldon-axis illuminator without a path element or an optical stop thatinterferes with the OCT path. In still further embodiments, theilluminator may include a fiber ring illuminator. In certainembodiments, the fiber ring illuminator may include a ring of opticalfibers that defines an annulus, the annulus having an inner diameter, anouter diameter and a radiant numerical aperture, the radiant numericalaperture being approximately 0.22 and between 0.16 and 0.28.

In some embodiments, the system further includes a collimating lensfollowing the fiber ring illuminator. An image of the ring illuminatormay be focused onto the vicinity of a pupil of an eye of a subject suchthat the outer diameter of the annulus imaged onto the pupil is lessthan a diameter of the pupil. The inner diameter of the annulus at thepupil plane may be less than a pupil diameter.

In further embodiments, the illumination portion may include a fixationtarget. In certain embodiments, the fixation target may include one ormore single-mode optical fibers, the output of the single mode opticalfibers displaced with respect to the output of the illuminator, suchthat the one or more single mode fibers is conjugate to the intermediateconjugate image plane of the OCT path.

In still further embodiments, the image capture portion may be furtherconfigured to provide a real-time video image to aid alignment of an OCTbeam; capture a photographic reference image of a sample to use as acomparison to an OCT depth-resolved image; enable full color orhyperspectral photography for emphasizing various features of an imagedstructure and various depths of the image structure; and/or enablefluorescent image photography for emphasizing various features of theimaged structure and various depths of the image structure.

In still further embodiments, hyperspectral images provide additionalclinical diagnostic value when correlated to depth resolved structuralOCT images.

In some embodiments, the illumination/fixation path includes a lightsource having a range of from about 650 to about 740 nm. In certainembodiments, the light source comprises a light emitting diode (LED).

In further embodiments, the OCT path may be coupled to the image capturepath though a polarization independent dichroic beamsplitter. Thedichrotic beamsplitter may be a thin film filter.

In still further embodiments, the system further includes a real-timerange finder configured to guide a photographer to a correct workingdistance, the working distance being relative to a subject's cornea.

In some embodiments, the system further includes an electromechanicalreference arm.

In further embodiments, the system is fitted within a compact housing,the housing including a cable tether to remainder of the OCT system, thehousing sized to provide a handheld system for imaging a sample.

Still further embodiments provide methods for imaging a sample in anoptical coherence tomography system, the OCT system including an OCTportion having an associated OCT path, an image capture portion havingan associated image capture path, different from the OCT path and anilluminator with an optional fixation target having an associatedillumination/fixation path, different from the OCT path and the imagecapture path. The method includes operating in an OCT only examinationmode; operating in an image capture only mode; operating in a combinedoperation mode; or operating in a short duration flash operation mode.

In some embodiments, operating the system in an image capture only modeincludes lowering the optical power of an OCT signal of the system; andincreasing the optical power radiating from a ring illumination source.The combined optical powers irradiating a subject across the imagingsequence remains below a maximum permissible exposure level.

In further embodiments, operating the system in the short duration flashoperation mode includes operating at an elevated power level for a brieftime period to acquire a snapshot, the elevated power level illuminatingthe subject at between 2 and 10 mW/cm².

In still further embodiments, an imaging cycle of the OCT system mayinclude operating in an image capture mode for exploratory examinationof a fundus with the OCT mode off in order to identify a region ofinterest; operating in a combined operation mode, wherein the OCT modeis operating in a two-orthogonal-axis aiming mode and the image capturemode is operating in low power mode as an alignment support device tolocate an OCT beam on a region of interest such that the combinedexposure remains below a maximum permissible exposure level; operatingin a short duration flash operation mode for a flash short duration highintensity image acquisition with an image capture device, the OCT modebeing off; and acquiring an OCT image sequence with low level videoillumination and digital image capture on or off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a conventional ophthalmic Fourierdomain optical coherence tomography (OCT) system.

FIG. 2 is a block diagram of an imaging probe in accordance with someembodiments of the present inventive concept.

FIG. 3 is a diagram illustrating an OCT imaging path in accordance withsome embodiments of the present inventive concept.

FIG. 4 is a diagram illustrating a digital video image capture path inaccordance with some embodiments of the present inventive concept.

FIG. 5 is a diagram illustrating a ring illuminator including fixationand a range finder in accordance with some embodiments of the presentinventive concept.

FIGS. 6A through 6C are diagrams illustrating an illuminator path inaccordance with some embodiments of the present inventive concept.

FIG. 7 is a timing diagram illustrating timing and intensity inaccordance with some embodiments of the present inventive concept.

FIGS. 8A and 8B are diagrams illustrating a display window in accordancewith some embodiments of the present inventive concept.

FIG. 9 is a diagram illustrating application of video eye tracking inOCT in accordance with some embodiments of the present inventiveconcept.

FIG. 10 is a diagram of a Spectral Domain OCT (SDOCT) system including arange finder in accordance with some embodiments of the presentinventive concept.

FIG. 11 is a flowchart illustrating operations of a range findingcontroller in accordance with some embodiments of the present inventiveconcept.

FIG. 12 is a block diagram illustrating a data processing systemconfigured in accordance with embodiments of the present inventiveconcept.

FIG. 13 is a more detailed block diagram of a data processing system ofFIG. 12 in accordance with some embodiments of the present inventiveconcept.

DETAILED DESCRIPTION

The present inventive concept will be described more fully hereinafterwith reference to the accompanying figures, in which embodiments of theinventive concept are shown. This inventive concept may, however, beembodied in many alternate forms and should not be construed as limitedto the embodiments set forth herein.

Accordingly, while the inventive concept is susceptible to variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit the inventive concept to the particular forms disclosed, but onthe contrary, the inventive concept is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinventive concept as defined by the claims. Like numbers refer to likeelements throughout the description of the figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising,” “includes” and/or “including” when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. Moreover, whenan element is referred to as being “responsive” or “connected” toanother element, it can be directly responsive or connected to the otherelement, or intervening elements may be present. In contrast, when anelement is referred to as being “directly responsive” or “directlyconnected” to another element, there are no intervening elementspresent. As used herein the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms used herein should be interpretedas having a meaning that is consistent with their meaning in the contextof this specification and the relevant art and will not be interpretedin an idealized or overly formal sense unless expressly so definedherein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement without departing from the teachings of the disclosure. Althoughsome of the diagrams include arrows on communication paths to show aprimary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Referring now to FIG. 1, a block diagram illustrating a conventionalFourier domain optical coherence tomography (FDOCT) ophthalmic imagingsystem will be discussed. As illustrated in FIG. 1, the system includesa broadband optical source 100 directed along a source path 101 to abeamsplitter 104 where the source radiation is divided into a referencepath 105 and a sample path 107. The reference light is returned througha reference reflection device 106 back through the beamsplitter 104where it mixes with the light returned from a sample, such as the retinaof an eye 111. The resultant wavelength dependent interferogram isdirected through a detection path 103 to a detection module 102. Thetotal spectral interferogram is processed using Fourier transforms toderive a spatial domain depth resolved image.

In contrast to a time domain OCT system, where the reference mirrorscans a range over time that matches the depth range of interest forimage the subject to acquire a temporal interferogram, the FDOCT systemacquires a spectral interferogram from a fixed reference position 113that is path length matched to a target axial position with respect tothe subject. The spectral interferogram contains information for alldepths within a window 114. The window is defined by parameters ofdetection as is known in the art. A scanning subsystem 108 includes apair of scanning galvo mirrors 109 and an objective lens set with focalcapabilities 110. For posterior, or retinal, ophthalmic imaging, thescanned OCT beam is directed through the pupil of the eye 112 to imagethe retina. An FDOCT system may include a serial acquisition of spectralinformation using a broadband swept frequency optical source, or aparallel acquisition of spectral information using a broadband lowcoherence source and a spectrometer, or a combination of these methods.A spectrometer based system is referred to as spectral domain opticalcoherence tomography (SDOCT) and a swept source system is referred toswept source OCT (SSOCT).

One of the difficulties in using an OCT system, and particularly ahandheld OCT system, to image, for example, the retina of the eye, isthat it is difficult to align, i.e. aim, the OCT beam through the pupil.Thus, according to some embodiments of the present inventive concept asystem is provided including an optical coherence tomography system, anillumination system for digital photographic imaging, a digital camerafor video photographic image capture, and an optional fixation target todirect the gaze of the patient.

A challenge to the design of a compact OCT scanning unit with anintegrated video photographic system is to provide passively alignedoptical paths, reducing the need for bulky electromechanical components,such that illumination, video focus, OCT focus and fixation focus areappropriately coordinated for all possible subjects without the need fordifferential focusing of the various optical subsystems.

Referring now to FIG. 2, a block diagram of a system in accordance withsome embodiments of the present inventive concept will be discussed. Asillustrated in FIG. 2, some embodiments of the present inventive conceptinclude a compact optical design comprising a scanning beam OCT path201, an illumination path 203 for support of digital video capture, anda video image capture path 202. As further illustrated, the systemfurther includes a polarization beam combiner 204 to couple theillumination and video capture paths, inhibiting specular reflectionsfrom the illuminator from interfering with the image of interest on thedigital video capture device. In some embodiments, the digital imagecapture path and the OCT are coupled through a dichroic beamsplitter205, share an intermediate conjugate image plane 206 path and a commonobjective lens 207 to image the subject of interest 208, for example aneye.

Referring now to FIG. 3, an OCT imaging path in accordance with someembodiments of the present inventive concept will now be discussed. Asillustrated therein, the OCT path includes a single-mode optical fiber301 terminated into a collimator 302, the collimated light directed to apair of orthogonally scanning galvo mirrors 303, the scanned beamdirected through a relay lens set 304 such that an image of the opticalfiber input is imaged telecentrically onto the intermediate commonconjugate plane (intermediate conjugate) 305. The image at theintermediate conjugate is then imaged onto the subject 307 with anappropriate objective lens 306. In some embodiments, the optical fiber301 is a Corning HI780 single-mode fiber, the collimator 302 has a 25.0mm focal length and the galvo mirrors 303 have a 5.0 mm or greater clearaperture. The relay lens set 304 includes a lens doublet pair with 2-200mm FL doublets for an effective FL of 100 mm operating at f/4.0. In someembodiments, the path length from collimator 302 to relay 304 is about93.4 mm, from the relay 304 to the intermediate conjugate 305 is about93.4 mm and from the conjugate 305 to the objective lens 306 is about20.7 mm (at emmetropia). The objective lens set 306 may be a 2×50 mm FL40 Diopter doublet pair with 25 mm effective FL, operating at 15 mmworking distance. The galvos 303 are conjugate to the pupil plane of theeye, and the output of the fiber 301 is conjugate to the retina.

One advantage provided by systems in accordance with embodiments of thepresent inventive concept discussed with respect to FIG. 3, is theability to incorporate a final imaging objective suited to imaging avariety of targets without modification of or relative motion betweenthe optical elements that precede the final imaging objective. Thesystem thus defined with appropriate selection of objective lens issuited to ophthalmic imaging of the posterior (retina) or anterior(cornea) of a human eye, ophthalmic imaging of small animal (e.g.rodent) eyes, or non-ophthalmic imaging. Because of the uniquechallenges to imaging of a retina, discussions of embodiments hereinwill largely focus on retinal imaging, but it will be understood thatembodiments of the present inventive concept are not limited to retinalimaging.

For retinal imaging, the wavelength of interest may be in the 800 nm to900 nm wavelength range, or may be in the 1000 nm to 1100 nm wavelengthrange. A condition for artifact free OCT imaging is that the opticalfiber operates in a single spatial mode at the wavelength of interest,which in turn typically requires that the second-order mode cutoffwavelength of the optical fiber be shorter than the imaging wavelength.A fiber such as Corning HI780 is suitable for imaging in the 800 nm-900nm band.

For OCT retinal imaging, the optical system comprises a relay systemwherein the galvo mirror scanning pair are located a back focal lengthfrom an optical relay lens set, the galvos 303 scan telecentrically atthe intermediate conjugate 305, and the conjugate of the galvos 303 isimaged a front focal length from the objective lens set 306 at thepupil. The lateral resolution at the retina is determined by the beamstop of the optical system, at the pupil of the eye. For mydriatic(dilated) imaging, this is not much of a constraint. For non-mydriatic(not dilated) imaging, the stop is approximately 3 mm, but additionalallowance must be made for off-axis aiming to explore peripheralfeatures of the retina. The entrance pupil of the system is defined bythe collimated beam at the galvos 303. In one embodiment of this system,there is a 4× demagnification of the beam between the entrance pupil(galvo) and stop (eye pupil) of the optical system. Thus, in someembodiments, the maximum galvo dimension for a 3.0 mm ocular pupil isabout 12.0 mm. An optical dimension to facilitate alignment through anon-mydriatic eye with allowance for steering of the beam is toconstrain the stop to one-half the ocular pupil, or about 1.5 mm. Thissets the galvo dimension at about 6.0 mm. Thus, in some embodiments, thestop of the OCT system may be constrained to between one-quarter andthree-quarter of the natural non-mydriatic pupil diameter, and thereforethe entrance pupil, or galvo diameter, to greater than about 3.0 mm andless than 12.0 mm.

The image of the optical fiber at the intermediate conjugate is a backfocal length from the objective lens 306 when set to image the retina ofan emmetropic subject. The scanning OCT beam is collimated exiting theobjective lens set 306 and is focused on the retina by the optics of theeye. Focal adjustment for imaging hyperopic or myopic subjects, or forintentionally modifying focus to emphasize structures that may not liewithin the photo-active layers of the retina, is accomplished by movingthe objective lens 306 with respect to the intermediate conjugate 305.

Referring now to FIG. 4, a diagram illustrating a digital video imagecapture path in accordance with some embodiments of the presentinventive concept will be discussed. As illustrated in FIG. 4, the videocapture path is designed to share the intermediate conjugate asdiscussed in commonly assigned United States Patent Publication No.2009-0141237, which has been incorporated by reference above. Consideredfrom the retina back to the image plane of the digital capture device,the retina is imaged to the intermediate conjugate through the objectivelens. The image at the intermediate conjugate then images back through arelay 314 to a lens system 311 with an aperture 313, and onto the imageplane of a digital camera 312. In symmetry with the OCT path, theaperture is conjugate to the pupil of the eye, and is set in relation tothe illumination as will be discussed below. The camera detector planeis conjugate to the retina. Sharing as it does the intermediateconjugate with the OCT path, the video capture is both coaxial to, andconfocal with the OCT path for all subjects, objectives and objectivefocal conditions. In some embodiments, the relay 314 includes a 2-300 mmFL doublet pair with a 150 mm effective FL operating at f/6.0. The relaymay be 122 mm from the intermediate conjugate, and 115 mm from thesurface of the camera lens.

The OCT path and the video capture path are coupled through a dichroicbeam splitter 205 as shown in FIG. 2 discussed above. The dichroicfilter acts as a high reflectivity mirror for the OCT signal and a hightransmissivity window for all wavelengths of the video system. Asdesigned, the dichroic filter is a thin film stack that operates withlow polarization dependence at 45 degrees, and is transmissive for allwavelengths from about 400 nm to about 740 nm, and is reflective fromabout 750 nm to about 950 nm, and is designed according to the known artof thin film optical filters. The dichroic filter is positioned betweenthe relay lens of the OCT path and the intermediate conjugate.

A challenge to the design of a compact OCT scanning unit with anintegrated video photographic system is to provide a wide fieldillumination system for video capture that does not suffer frominterfering specular reflections and whose optics neither increasesystem bulk nor adversely impact the OCT imaging.

Illumination systems for fundus photography are well known, anddescribed for example in U.S. Pat. No. 5,455,644; Fundus camera systems:a comparative analysis by DeHoog et al. (Applied Optics 48, No. 2, 2009.pp 221-228); and Optimal parameters for retinal illumination and imagingin fundus cameras by DeHoog et al. (Applied Optics 47, No. 36, 2009.Pp6769-6777). As described by Dehoog et al., there are two basicapproaches to illumination in fundus photography: external and internal.These solutions are described for fundus photography alone, not incombination with OCT. These techniques, when combined with OCT,typically require an annular mirror with clear aperture equal to thediameter of the scanned OCT beam, for example, at the intermediateconjugate; necessarily such apertures in the OCT path increase the formfactor of the optical system, since the outer diameter of the imagingclear aperture defines the inner diameter of the annular mirror. Inother words, to maintain a compact form factor the OCT scanning widthmust be constrained, and this scan width directly translates to field ofview.

U.S. Pat. No. 5,822,036 to Massie discusses a more compactimplementation of an external illumination system using ringillumination directed through a contact lens in intimate contact withthe subject cornea; the ring illumination is mediated through opticalfibers positioned along the distal perimeter the objective lens. Thisstructure is not amenable to coupling to the non-contact OCT imager ofthe present inventive concept.

U.S. Pat. No. 5,506,634 to Wei discusses a combined OCT system withfundus imager. However, this system utilizes external, off-axisillumination which does not lend itself well to wide field illuminationor compact form factor. U.S. Pat. No. 7,140,730 to Wei discusses anon-axis external illumination method, whereby an illumination sourcebehind an aperture projects to a beamsplitter that couples theillumination path to the image capture path. This system hasdisadvantages in number of optical elements, lack of control of field ofillumination on the retina, and interference of the illumination pathwith the image capture path. Therefore, it is not generally possible toat once create a compact and wide-field combined OCT plus fundusphotography using the guidance of the fundus camera prior art.

Commonly assigned United States Patent Publication No. 2009-0141237 toIzatt, incorporated by reference above, illustrates the use of anannular illuminator polarization multiplexed into a common path with theimage capture device. Thus, some embodiments of the present inventionprovide a compact wide field illuminator that interferes with neitherthe OCT path nor the image capture path, yet provides uniform wide fieldillumination without feeding back specular reflections from the corneato the image capture device. Furthermore, the illumination architectureprovides other advantages in terms of spectrum and intensity control, aswell as manufacturability as will be discussed further below.

FIG. 5 is a diagram of a ring illuminator in accordance with someembodiments of the present inventive concept will be discussed. FIGS. 6Athrough 6C are diagrams illustrating an illumination path in accordancewith some embodiments of the present inventive concept. As illustratedin FIG. 5, the fiber ring defines an annulus with an inner diameter, anouter diameter, and a radiant numerical aperture. As illustrated in FIG.6A, the ring illuminator 321 is followed by a collimating lens 322, andthe image of the ring illuminator is focused onto the pupil of thesubject eye such that the outer diameter of the annulus imaged onto thepupil is less than the pupil diameter, and there remains an innerdiameter of the annulus in the pupil plane. As etendue of an opticalsystem is conserved (with appropriate consideration of refraction),there remains a deterministic relationship between the annulusdimensional magnification (demagnification) and the numerical aperturedemagnification (magnification) at pupil plane. The numerical apertureat the pupil plane defines the field of illumination. By selectingappropriate ring diameters, fiber types (numerical aperture) andmagnification, one can control the field of illumination as well asoperating conditions, such as mydriatic (dilated) or non-mydriatic (notdilated) imaging. In some embodiments, the magnification is 1:1.09, theannular ring diameter is 2.2 mm at core center and as imaged at thecornea 324, the fibers are multimode with a core diameter of 100 μm,cladding diameter of 125 μm and a numerical aperture of about 0.22. Theresultant system is suitable for non-mydriatic imaging (outer annulusdiameter 325 of 2.5 mm at the pupil less than 3.0 mm optical stop) andwide field imaging (greater than about 60 degrees) illumination coverageat the retina. Illumination pattern 326 for two circumferentiallyopposed fibers on the retina in a human eye model of system performanceis shown in FIG. 6B and en face in FIG. 6C. Additionally, theversatility of this illumination and imaging system is shown by theillumination pattern on a mouse retina, where the only difference in thesystems is in the objective lens. The objective lens design is optimizedfor the spherical, or ball-lens, phenotype of the rodent, as describedin commonly assigned United States Patent Publication No. 2009-0268161,incorporated by reference above. Further still, the illumination systemprovides uniform illumination when used in conjunction with atelecentric objective lens, for illumination of a cornea or other tissuestructure that is preferably imaged with a telecentric imaging system.

The digital video capture subsystem in accordance with some embodimentsdiscussed herein serves multiple purposes. The first purpose is toprovide a real-time video image to aid the alignment of the OCT beam.For this application, low level optical irradiance is desired to keepthe total irradiance at the retina below the Maximum PermissibleExposure (MPE) for eye safe operation over extended imaging periods. Themaximum permissible exposure (MPE), as defined in the American nationalstandard for safe use of lasers (ANSI Z136.1), is a function ofwavelength and optical power. It is desirable to illuminate in theinfrared or near-infrared with a minimum optical power. Particularlywhen the OCT system is scanning simultaneously with the videoillumination, the video illumination will be at the lowest levelsuitable to derive an image suitable for alignment.

The second purpose of the digital video capture subsystem is to use thedigital video image for exploratory ophthalmoscopy. In this mode, theOCT signal may be turned off, and the radiant power of the videoillumination turned up to facilitate higher contrast imaging. In thismode, the system functions as a non-contract fundus camera.

A third purpose is to capture a photographic reference image againstwhich to compare the OCT depth-resolved image. The low-level alignmentsignal and the intermediate level exploratory signal may be sufficientto capture a nominal reference image. It may also be desirable toprovide a significant increase in optical irradiance for a shortinterval in order to capture a brighter or higher contrast image.Furthermore, it may be desirable to provide visible illumination duringthe period of image capture in order to provide a color photograph asclinical record.

The fiber ring illuminator enables flexible placement and selection ofthe light source or light sources remote from the scan head, furthersupporting compact design of the scan head. Additionally, the remotecoupling of the light source simplifies electronic design and reducescomplexity of electrical systems and power delivery within the scanhead. The development of light emitting diode (LED) technology hassimplified the selection and management of illumination sources. In someembodiments, a single LED is used at a wavelength between about 650 nmand about 740 nm coupled into a fiber bundle at the proximal end of thefiber ring illuminator cable. In these embodiments, the bundle consistsof fifty-five multimode optical fibers bundled together at the proximalend of a cable, and distributed into a ring at the distal end. A 30 mWLED is sufficient including coupling losses to provide the desiredilluminance on the retina, though lower powers may also be acceptable.The integrated optical output power from the objective lens may beconstrained to 50 μW, so that when combined with 700 μW of OCT power theMPE for long term exposure (30,000 seconds) is not exceeded. The 50 μWpower level is sufficient to provide a visible image of the retina atvideo rates.

The near-infrared illumination at low power level is satisfactory forexploration and alignment using the digital video signal. However,higher intensity is desirable for higher contrast and higher signal tonoise images. In some embodiments of the present inventive concept, theillumination intensity level may be raised, and the exposure on thedigital capture device adjusted according to well known means in orderto capture and display a higher quality image.

In order to keep the system operating within the MPE for the desiredexamination period, the system operation allows an OCT-only examination,a video image capture period only, a combined operation mode, and ashort duration flash operation mode of the digital imaging system.Combined operation is discussed above. In video capture only mode, theOCT signal may be turned down or off, and the ring illumination sourceturned up to 500 μW, the precise level determined in conjunction withthe sensitivity of the image capture device, the turbidity of theoptical medium, and the desired exposure period. In flash digital imagecapture mode, a brief cycle of elevated power, for example 5 mW, or 2-3W/cm², to acquire a snapshot may be applied.

A particular imaging cycle may consist of the following: exploratoryexamination of the fundus in video image capture mode, with OCT off toidentify a region of interest; combined operation mode, with the OCToperating in a two-orthogonal-axis aiming mode and the video imagecapture operating in low power mode as an alignment support device, inorder to locate the OCT beam on the region of interest; a flash shortduration high intensity image acquisition with the digital image capturedevice, OCT signal off, followed by an OCT image acquisition sequencewith low level video illumination and digital image capture on or off,as desired. This is illustrated in the timing and intensity diagram ofFIG. 7. It will be understood that other imaging sequences are possibleand may be established as pre-programmed sequences or may bephotographer controlled.

A third purpose of the video capture subsystem is to enable full coloror hyperspectral photography for emphasizing various features of theimaged structure and various depths of the imaged structures, suchhyperspectral images providing additional clinical diagnostic value whencorrelated to the depth resolved structural OCT images.

A fourth purpose of the video capture subsystem is to enable fluorescentimage photography for emphasizing various features of the imagedstructure and various depths of the imaged structures, such fluorescentimages providing additional clinical diagnostic value when correlated tothe depth resolved structural OCT images.

It is well understood in the art that full color imaging is desirable toprovide diagnostic images consistent with clinical expectations, forexample as derived from indirect ophthalmoscopy and historicalexpectations from a generation of film-based fundus photography. It istherefore desirable to present an imaging mode consistent with the art,and further to provide correlated imaging between such video fundusphotographs and the depth-resolved information provided by OCT.

In some embodiments of the inventive concept imaging optics areoptimized for high-quality OCT images, that is an independent OCT paththat couples to the video imaging path through a polarizationindependent dichroic beamsplitter, which may be a thin film filter. Theimaging objective is optimized for high resolution color-correctedimaging of the OCT signal. Additionally, the dichroic beamsplitter istransmissive without significant color centers for all visiblewavelengths shorter than the reflection edge, as discussed above. Theimaging objective must also be transmissive for the illumination anddigital image capture wavelengths, thus the imaging objectives arebroadband antireflective coated, for example, from about 400 nm to about950 nm. As discussed, the lateral resolution of the digital imagecapture subsystem may be suboptimal when the system is optimized for theOCT imaging. While high performance broadband imaging optics may bedesigned, there will in general be some trade-off to be made in choiceof best performance operating range and cost. It is understood that thetrade-off to optimize for superior OCT imaging at some cost to thedigital image capture is one of many choices.

With the broadband transmission defined, it then is desirable to offerspecific flexibility to select illumination wavelengths. One option isto illuminate directly with halogen or Xenon lamps coupled into theproximal end of the illuminator bundle. Another convenient choice is touse the new generation of white light LEDs. Another convenient choice isto use a multiplicity of monochromatic sources, such as would beavailable by filtering the output of a halogen or Xenon lamp, or byselecting from available monochromatic LEDs. On such choice of LEDswould be to illuminate with a combination of a blue, a green and a redLED. This combination may be used in unison, or cycled in a sequence,and may be captured in a black & white camera or a color camera.

Fundus Image Colorimetry in accordance with some embodiments will bediscussed Inherent in both the Fundus Illumination System and the FundusIllumination Light Guide is the ability to accommodate a wavelengthrange of about 400-1000 nm with no change to the design parameters. Thusmultispectral imaging of the fundus or other target tissue is possible.Given that light penetration into tissue in general, and the retinaltissue specifically, is wavelength dependant, a series of images can bebuilt up using selective wavelength to create a visual depth volume. Inaddition, selective wavelength imaging at a specific depth within theretina may be used to create a visual filtering of the fundus image tolocate pathologies to better guide the OCT scanning. Adding amonochrometer input to the illumination system or other wavelengthselection mechanism such as turning on or adjusting the power level ofindividual monochrome LEDS provides the capability to “dial” thru thewavelength range while viewing the live fundus image to see ifpathologies of interest appear could be of great value. This functiondubbed “ChromaFundus” would allow the operator to selectively match theOCT image with a corresponding Fundus image taken at a selectedwavelength. Likewise, if the source were scanned through the wavelengthrange the display aspect of such data could result in the multispectralimages stacked just as the OCT data and depth windowing could be used todisplay pathologies of interest.

In general, a black&white camera will offer greater imaging resolution.A cycled acquisition of monochromatic images may be captured, and apseudo-colored image recreated in post-processing by creating a weightedaverage image from the multiplicity of monochrome images. An appropriatecamera is the Imaging Source DMK 72BUC02 monochrome CMOS camera. ThisFundus Image Colorimetry has many advantages in the ability to obtainthe highest quality image per exposure, and to tune the color quality tomeet clinical objectives. One such objective is to obtain images with acolor temperature similar to accepted commercial clinical systems.

The combination of design elements, including passive registration ofthe digital video illumination optical path, the digital video imagecapture path, and the OCT path, supports real-time coordination of theOCT region of interest to pathologies observed on the digital imagecapture device.

Referring now to FIG. 8, display windows in accordance with someembodiments will be discussed. As illustrated in FIG. 8, such a systemand method include an image presentation window for the OCT aiming modeimage, with horizontal 501 and vertical 502 orthogonal views and animage presentation window for the digital image capture image mode 503,together with another window for presentation of an en face intensityprojection of OCT depth resolved data 505. As discussed, the OCT anddigital image may be simultaneously live (in contrast to SLO images thathave a longer duration capture period). Dynamic Scan Control isfacilitated through a graphical box 504 overlaid on the video capturewindow that shows the sub region of the video field of view that is thecurrent OCT field of view. The photographer may dynamically control theOCT field of view—central location and extent of field of view—bydragging the location and boundaries of the graphical box overlay. TheOCT scanners are configured to respond in real-time, and the resultantOCT image aiming mode will update automatically in real-time. When thefinal region of interest is identified, the OCT image capture isinitiated, and the image is then acquired precisely on the region ofinterest as observed on the digital image capture device. The image sodisplayed on the video image capture device may be any of the modesmentioned, including a monochromatic image acquired at any one of theavailable illumination wavelengths, a true-color image derived fromwhite light illumination or selected color combination, or a compositecolor image acquired and derived by a combination of wavelengths.

The ability to control illumination wavelengths enables videofluorescence imaging, and in particular simultaneous OCT, Doppler OCT asdiscussed in U.S. Pat. No. 6,006,128, and fluorescence imaging. Thissynergy provides coordinated information on the structure of the tissue,the flow in the retinal vasculature, pooling of blood, presence offluorescent labels, and presence or lack thereof of natural fluorescentchromophores that have clinical diagnostic value. In some embodiments, afilter wheel is added in front of the digital camera, for example in theproximity of the aperture, a position of minimum filter surface area,and therefore size and cost. The filter wheel comes at no cost to theOCT performance.

A 480 nm fluorescence source is incorporated into the selection ofillumination sources to support both fluorescien imaging, forfluorescien angiography (FA), for example, and also in support ofauto-fluorescence (AF) imaging. The source output set to 2 mW/cm² on theretina is sufficient for excitation as discussed in Noninvasive Imagingand Monitoring of Retinal Pigment Epithelium Patterns using FundusAutofluorescence—Review by Framme, et al (Current Medical ImagingReviews, 2005, no. 1, pp 89-103). For FA, an emission filter with a530±43 nm bandpass at the camera aperture plane is appropriate. For AF,a long pass filter passing wavelengths longer than 500 nm isappropriate. Other sources of excitation and emission filters may beappropriate for imaging of other labels and chromophores.

In addition to coordinated focal requirements of the OCT and videocapture capability of the subject device, it is desirable to providecertain image stabilization features for the system, particularly forhandheld operations.

SLO has been used to stabilize OCT image location, for example, inUnited States Patent Publication No. 2010/0053553 to Zinser, and pupiltracking has been used to for eye tracking using video technology. Adisadvantage of SLO-based eye tracking is that image acquisition isrelatively slow (e.g. 1 second per en face frame). A disadvantage ofpupil-based eye tracking for retina imaging is that the image recorded(e.g. the pupil) is not the same as the target image (e.g. the retina).

Therefore, an additional application of the video image is to providelow-latency feedback to the OCT scan position for image stabilization.One useful mode for providing this feedback is to identify and lock onto the optic nerve head, tracking changes to the optic nerve head withinthe image frame, and utilizing this changing position to direct the OCTscanners.

Eye Tracking will now be discussed. As the subject eye moves the imageon the digital image capture window moves. The motion within this windowis tracked using methods known in the art. For example, a well definedlandmark, such as the optic nerve head, is software-identified in amanner similar to pupil tracking algorithms. During aiming mode, avector is computed that identifies the relative position of the OCTregion of interest to the landmark. This vector may be recomputed duringaiming mode as the region of interest is modified through manipulationof the dynamic scan control graphical box. During OCT image capturemode, relative motion between the scan head and the patient will causemotion of the position of the landmark. At this point the vector isfixed, and a signal is sent to the OCT scanning mirrors to adjust theposition of the acquisition window such that the relative position ofthe OCT field of view and the landmark observed on the digital capturedevice remains stable. This behavior is illustrated for example in FIG.9. As illustrated therein, in the video window 514, the softwareautomatically identifies the optic nerve head (ONH) and draws a circle515 around the ONH. The user draws a box 517 around the region ofinterest, and the system scans the region as shown in B-scan 513 and enface view 518. The system computes a vector 516, and as the ONHidentifier 515 moves, a change vector (not shown) is applied to the OCTgalvos to keep the position of the region of interest stable.

An interferometer stabilization feature will now be discussed. OCT is aninterferometric system, and Fourier domain OCT (FDOCT) in particularrequires coordination and maintenance of a sample arm length and areference arm length.

Additionally, the sample arm length includes the working distancebetween the objective lens and the subject. It is therefore desirable toprovide the photographer with an indicator of current working distancewith respect to the target working distance.

Referring now to FIG. 10, an SDOCT system in accordance with someembodiments of the present inventive concept will be discussed. TheSDOCT system includes a supplemental time-domain rapid scanning opticaldelay (RSOD) system. As illustrated in FIG. 10, the SDOCT systemincludes a Beam Splitter (BS) 402, a first reference Arm (R1) 404 forretinal imaging, a second RSOD Reference Arm (R2) 408 for cornealimaging, a Mirror (M), a Diffraction Grating (DG) 406, RSOD objectiveLens (L) 407, RSOD mirror angle (s), Sample signal from retina (S1),Sample signal from cornea (S2), Point Detector (D1) 411 for capturingthe fundamental through the diffraction grating, and SDOCT arraydetector (D2) 410.

Correct location of the imaging lens relative to the patient's corneamay reduce vignetting and ensure accurate lateral calibration of theimage. In embodiments illustrated in FIG. 10, a real-time range finderis used to guide the photographer to the correct working distance. Asecond reference light path R2 404 matched to the design workingdistance enables detection of the corneal surface. The second referencepath 404 is part of a time domain OCT system that shares the opticalpath with the primary imaging Fourier domain OCT system. A scanningreference path, for example, a Rapid Scanning Optical Delay Line (RSOD)405 (Kwong et al, Optics Letters, 18, no. 7, 1993, pp. 558-560) in R2 ispath-length matched to the working distance, and scans through a 1.0 cmdistance for corneal ranging. As R2 scans, the time averaged signal atthe detector has a peak at the cornea. A visual or audio directionalindicator in the software may indicate the position of the cornearelative to the probe tip; as the probe approaches the designed workingdistance, the corneal peak will be strongest, and the visual or audiocue to the operator will indicate that the proper working distance hasbeen achieved.

In some embodiments, the RSOD may be designed with the followingparameters: for an angle σ of 22.5°, a mirror offset 408 of 3.2 mm, anobjective 407 focal length of 50 mm, a center wavelength of 840 nm, agrating 406 pitch of 600 lines/mm, and the path length swept by the RSODis 10 mm. A sweep rate of greater than 30 kHz is practical but notnecessary; a 100-200 Hz update rate should be sufficient, indicating alower cost scanning mirror will be sufficient for the range finder.

In some embodiments, the range-finder shares the primary OCT source 401and optical path 402 as shown in FIG. 10, with a fraction of the lightin the reference arm peeled off from the primary Fourier domainreference arm by a beamsplitter 403 to the time domain, e.g. RSOD,reference arm. Between 25% and 50% of the primary reference arm powermay be diverted to the time domain path without adversely impacting theprimary imaging OCT system, as generally the reference arm path isattenuated, particularly in an ophthalmic OCT system. The range findingand Fourier domain OCT paths are sufficiently separated such that nomixing between the two paths will occur, but care must be taken to matchthe pathlengths S2 (sample path to the cornea) and R2 such that thesignal from the cornea does not interfere with the retinal image. Thesignal from the cornea 412 will be very weak when the objective lens isset to imaging the retina 413. This is satisfactory for range finding,as the relatively slow refresh rate allows sufficient averaging to pullout the weak signal, and since this range finding is not for imagegeneration, and range finding accuracy can be to the millimeter level,the system can tolerate significantly more noise than would beacceptable in an imaging system.

This method uses the OCT light to determine the distance to the corneaand thus does not require an external light source or additional poweron the eye. There is no change to the sample arm optics or probe, whilethere is a moderate change to the spectrometer. Generally, highefficiency gratings 409 are used in spectrometer design, and theundiffracted fundamental diffraction order is cast onto a light trap toavoid stray light hitting the array detector 410. For the range finder,this fundamental order is directed to a point detector 411 in the bodyof the spectrometer, rather than a light trap. In one embodiment,approximately 3% of the sample light is lost through specular reflectionoff the cornea, and this becomes the light for range finding. 5% to 20%of the signal incident on the spectrometer is captured on the rangefinding detector, and demodulated with techniques well known in the timedomain OCT art.

In further embodiments, the range finder and the OCT imaging system areat different wavelengths, and the range finder signal couples to OCTsignal through the dichroic filter; the range finder signal may be at anear-infrared wavelength nominally shorter than the OCT signal. In orderto focus the range finding signal preferentially on the cornea, a singlemode fiber 333 with 0.12 NA is positioned within the clear aperture ofring illuminator of FIG. 5, with the distal end position placed adistance of 3.7 mm 335 behind the illumination fiber ring; in thisgeometry the range finding signal focuses directly on the cornea of theeye with a spot diameter on the cornea is approximately 60 μm.Construction of the ring illuminator to incorporate the independentranging signal as well as a fixation light 332 (discussed below) isshown in FIG. 5.

A combined time domain-spectral domain system for monitoring changes tothe front position of the eye in an eye length measurement device isdiscussed in U.S. Pat. No. 7,400,410 to Baker. In contrast to Baker, theembodiments of the present inventive concept is directed towardsproviding guidance to the photographer for correct positioning of theOCT imaging probe to the target in order to maximize image quality byminimizing vignetting through the subject pupil. In contrast to Baker,some embodiments of the present inventive concept allow full rangescanning of the retina, whereas Baker is designed for a pointmeasurement in order to measure a length of the eye, not the use of thecombined technologies for ranging or for ranging plus imaging.

Referring now to FIG. 11, methods for a complete control architecturethat includes range guidance in accordance with some embodiments of thepresent inventive concept is illustrated in a flowchart. Range findingis intended as an alignment aid for either or both of the OCT imagingsubsystem and the digital video imaging subsystem, both of which benefitthrough minimized vignetting at a proper working distance.

Operations of systems in accordance with some embodiments of the presentinventive concept will be discussed with respect to FIG. 11. Asillustrated in FIG. 11, after the software is started, operations beginat block 1100 by inputting information with respect to the subject to beimaged. The information may include, for example, age of the subject,eye length of the subject and the like. Operations continue at block1105 by automatically setting the initial reference arm position. Therange finder is initiated (block 1110). The user aims the probe (block1115) and it is determined if the probe is within the imaging range(block 1120). If it is determined that the probe is not within theimaging range (block 1120), operations return to block 1115 and repeatuntil it is determined that the probe is within range (block 1120). Ifit is determined that the probe is within range (block 1120), operationscontinue to block 1125 for a visual indicator. The retina image ismanually located (block 1130), and location confirmed using, forexample, a foot pedal. Once the reference image is located (block 1130),reference tracking is turned on (block 1135). An image is located withinthe depth field (block 1140). The reference arm position isautomatically adjusted to the center image in the depth (block 1145).

Tracking signal is analyzed to assure that the tracking remains withinrange by testing the tracking signal against a threshold (block 1150).If it is determined that the threshold has not been exceeded, operationscontinue to block 1165 where the focus is manually optimized. The fieldof view (FOV) is set using, for example, dynamic scan control using, forexample, a mouse, a touch screen, a foot pedal, or an on-probe control(block 1170). The scan is acquired (block 1175) and saved (block 1180).Using, for example, a pedal, the system is advanced to the next scan inthe protocol. It is determined if the last scan had been acquired (block1190). If it is determined that the last scan has been acquired, theacquisition is finished (block 1195).

If it is determined at block 1150 that the threshold has been exceeded,operations proceed to block 1155 where it is concluded that tracking hasfailed. The reference arm position is set (block 1160) and operationsreturn to block 1135 and repeat until the tracking signal has not beenexceeded (block 1150).

Another variable in the interferometric system that makes up OCT isfinding and controlling the reference path length to match the samplepath length. In time domain OCT, the reference arm always scans throughthe path matching conditions by design. Fourier domain systems operatedifferently, with fixed reference paths designed such that the pathmatching condition that produces an undesired DC signal is positionedconscientiously with respect to the depth range of interest. For imagingof mature eyes or anterior surface structures, variability of referencearm positions has not generally been a practical problem. Even for thevariability of mature eye lengths in an adult population, this has notbeen a problem in tabletop imaging where range finding and vignetting isnot a challenge, and where eye dilation is common. Reference armoptimization in handheld imaging, and particularly in pediatric imagingas well as in cases of severe eye distortion, for example in severemyopia, is more of a problem.

The use of range finding assures proper location of the objective lenswith respect to subject eye, assuring that pivot of the scanning galvosis conjugate to the pupil for the maximum scan range on the retina. Thefirst surface of the retina, the Inner Limiting Membrane (ILM), thelayer between the inner retina and the vitreous, is visible with highcontrast to the vitreous. This boundary layer is readily identified inline-wise (A-scan) signal processing by searching for the first positiveintensity gradient above a noise threshold at a search position startinga prescribed and slight distance away from the DC signal (for example 20pixels or 60 micrometers); the position of this ILM may be fed back toan electromechanical controller for the reference arm, assuring optimumstable positioning of the retina in the Fourier domain imaging window.The electromechanical control of the reference arm can be guided by theposition of the ILM on a single A-scan, by an operation, such asaveraging, of the position of the ILM on a multiplicity of A-scans, orby a centroid position of tissue in a region above, below, orsurrounding the identified ILM on a single A-line or multiplicity ofA-lines, as examples.

The combination of range finding plus reference arm control increasesthe likelihood of optimum image acquisition even with thephotographer-to-patient relationship is not perfectly stabilized.Furthermore, the eye length may be directly inferred from the rangereference arm position and the image reference arm position. This isparticularly useful for accurate lateral calibration of the retinalimage. In general, the scanning system is calibrated by determining thedegrees of deviation of the mirror per unit of applied voltage, and anestimate of eye length is used to convert the angular scan range to alateral value on the surface of the retina. In some embodiments of thepresent inventive concept, real-time knowledge of the scanner positionand eye length is used to accurately calibrate the lateral scan rangeduring imaging.

It may be further desirable to provide a fixation target to direct thegaze of the subject. As discussed in U.S. Patent Publication No.2009-0141237, a dichroic filter is used to separate the path of avisible fixation display, for example, an OLED or LCD display, inphysical space and in wavelength space, from the OCT, and videoillumination and capture paths. Such a configuration remains useful forproviding general fixation guidance as well as video stimulationsignals. Video signals in such a capacity may be useful for maintainingthe attention of the subject, and could also be used as a stimulationsignature in cooperation with a multifocal electroretinography (ERG)session to measure electrical activity related to retinal stimulation.

An internal fixation target is ubiquitous in tabletop SDOCT systems andtypically consists of a bank of LEDs or a screen to provide a target onwhich the patient can focus during imaging. Addition of an internalfixation target facilitates alignment in pediatric patients capable offixation.

In some embodiments, a point-fixation target is provided in a simplifiedstructure. It is important to maintain a central gaze, preferably withthe subject eye focused at infinity, to capture quality images centeredof the macula centered on the fovea. As shown in FIG. 5, a centralfixation target 332 may be collocated in the aperture of the ringilluminator. Such a configuration has multiple benefits, including theelimination of a separate dichroic or additional optical paths elements.

For the illuminator system described, a 0.12 NA single mode fiber orring of fibers, as shown in FIG. 10, recessed a distance of 6.6 mm 334behind the illumination fiber ring. The illumination of the fixationfiber bundle can be sequenced to occur after the fundus image is takenso the corneal reflection will not affect the fundus image. The funduscamera and fixation fiber illumination are mutually exclusive. In thisinstance, the imaged spot diameter on the retina is approximately 175um. A ring of fibers with an image diameter of approximately one half ofa millimeter focused at infinity provides a comfortable central fieldfixation target for a patient.

Some aspects of the present invention may be implemented by a dataprocessing system. Exemplary embodiments of a data processing system1230 configured in accordance with embodiments of the present inventionwill be discussed with respect to FIG. 12. The data processing system1230 may include a user interface 1244, including, for example, inputdevice(s) such as a keyboard or keypad, a display, a speaker and/ormicrophone, and a memory 1236 that communicate with a processor 1238.The data processing system 1230 may further include I/O data port(s)1246 that also communicates with the processor 1238. The I/O data ports1246 can be used to transfer information between the data processingsystem 1230 and another computer system or a network using, for example,an Internet Protocol (IP) connection. These components may beconventional components such as those used in many conventional dataprocessing systems, which may be configured to operate as describedherein.

Referring now to FIG. 13, a more detailed block diagram of a dataprocessing system of FIG. 12 is provided that illustrates systems,methods, and computer program products in accordance with someembodiments of the present invention, which will now be discussed. Asillustrated in FIG. 13, the processor 1238 communicates with the memory1236 via an address/data bus 1348, the I/O data ports 1246 viaaddress/data bus 1349 and the electronic display 1339 via address/databus 1350. The processor 1238 can be any commercially available or customenterprise, application, personal, pervasive and/or embeddedmicroprocessor, microcontroller, digital signal processor or the like.The memory 1236 may include any memory device containing the softwareand data used to implement the functionality of the data processingsystem 1230. The memory 1236 can include, but is not limited to, thefollowing types of devices: ROM, PROM, EPROM, EEPROM, flash memory,SRAM, and DRAM.

As further illustrated in FIG. 13, the memory 1236 may include severalcategories of software and data used in the system: an operating system1352; application programs 1354; input/output (I/O) device drivers 1358;and data 1356. As will be appreciated by those of skill in the art, theoperating system 1352 may be any operating system suitable for use witha data processing system, such as OS/2, AIX or zOS from InternationalBusiness Machines Corporation, Armonk, N.Y., Windows95, Windows98,Windows2000 or WindowsXP, or Windows CE or Windows 7 from MicrosoftCorporation, Redmond, Wash., Palm OS, Symbian OS, Cisco IOS, VxWorks,Unix or Linux. The I/O device drivers 1358 typically include softwareroutines assessed through the operating system 1352 by the applicationprograms 1354 to communicate with devices such as the I/O data port(s)1246 and certain memory 1236 components. The application programs 1354are illustrative of the programs that implement the various features ofthe some embodiments of the present invention and may include at leastone application that supports operations according to embodiments of thepresent invention. Finally, as illustrated, the data 1356 may includedata acquired using the OCT imaging module 1365, which may represent thestatic and dynamic data used by the application programs 1354, theoperating system 1352, the I/O device drivers 1358, and other softwareprograms that may reside in the memory 1236.

As further illustrated in FIG. 13, according to some embodiments of thepresent invention, the application programs 1354 include OCT imagingmodules 1365. While the present invention is illustrated with referenceto OCT imaging modules 1365 as being application programs in FIG. 13, aswill be appreciated by those of skill in the art, other configurationsfall within the scope of the present invention. For example, rather thanbeing application programs 1354, these circuits and modules may also beincorporated into the operating system 1352 or other such logicaldivision of the data processing system. Furthermore, while the OCTimaging modules 1365 are illustrated in a single system, as will beappreciated by those of skill in the art, such functionality may bedistributed across one or more systems. Thus, the present inventionshould not be construed as limited to the configuration illustrated inFIG. 13, but may be provided by other arrangements and/or divisions offunctions between data processing systems. For example, although FIG. 13is illustrated as having various circuits, one or more of these circuitsmay be combined without departing from the scope of the presentinvention.

It will be understood that the OCT imaging modules 1365 may be used toimplement various portions of the present invention capable of beingperformed by a data processing system. For example, the OCT imagingmodules may be used to process and assess the images produced by the OCTsystem according to some embodiments of the present invention.

Example embodiments are described above with reference to block diagramsand/or flowchart illustrations of methods, devices, systems and/orcomputer program products. It is understood that a block of the blockdiagrams and/or flowchart illustrations, and combinations of blocks inthe block diagrams and/or flowchart illustrations, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, and/or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer and/or other programmable data processingapparatus, create means (functionality) and/or structure forimplementing the functions/acts specified in the block diagrams and/orflowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the functions/acts specified in the block diagrams and/orflowchart block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer-implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe block diagrams and/or flowchart block or blocks.

Accordingly, example embodiments may be implemented in hardware and/orin software (including firmware, resident software, micro-code, etc.).Furthermore, example embodiments may take the form of a computer programproduct on a computer-usable or computer-readable storage medium havingcomputer-usable or computer-readable program code embodied in the mediumfor use by or in connection with an instruction execution system. In thecontext of this document, a computer-usable or computer-readable mediummay be any medium that can contain, store, communicate, propagate, ortransport the program for use by or in connection with the instructionexecution system, apparatus, or device.

The computer-usable or computer-readable medium may be, for example butnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, device, or propagationmedium. More specific examples (a non-exhaustive list) of thecomputer-readable medium would include the following: an electricalconnection having one or more wires, a portable computer diskette, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,and a portable compact disc read-only memory (CD-ROM). Note that thecomputer-usable or computer-readable medium could even be paper oranother suitable medium upon which the program is printed, as theprogram can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted, orotherwise processed in a suitable manner, if necessary, and then storedin a computer memory.

Computer program code for carrying out operations of data processingsystems discussed herein may be written in a high-level programminglanguage, such as Java, AJAX (Asynchronous JavaScript), C, and/or C++,for development convenience. In addition, computer program code forcarrying out operations of example embodiments may also be written inother programming languages, such as, but not limited to, interpretedlanguages. Some modules or routines may be written in assembly languageor even micro-code to enhance performance and/or memory usage. However,embodiments are not limited to a particular programming language. Itwill be further appreciated that the functionality of any or all of theprogram modules may also be implemented using discrete hardwarecomponents, one or more application specific integrated circuits(ASICs), or a field programmable gate array (FPGA), or a programmeddigital signal processor, a programmed logic controller (PLC), ormicrocontroller.

It should also be noted that in some alternate implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved. Moreover, the functionality of a given block of the flowchartsand/or block diagrams may be separated into multiple blocks and/or thefunctionality of two or more blocks of the flowcharts and/or blockdiagrams may be at least partially integrated.

In the drawings and specification, there have been disclosed exemplaryembodiments of the invention. However, many variations and modificationscan be made to these embodiments without substantially departing fromthe principles of the present invention. Accordingly, although specificterms are used, they are used in a generic and descriptive sense onlyand not for purposes of limitation, the scope of the invention beingdefined by the following claims.

That which is claimed is:
 1. A system for imaging a subject, the systemcomprising: two imaging paths, a scanning beam optical coherencetomography (OCT) imaging path and a video imaging path, wherein thescanning beam OCT imaging path comprises: a source of broadband opticalradiation; a beamsplitter dividing the source of broadband opticalradiation into a reference path and a sample path; and a beamsplitterthat mixes source light reflected from the subject in the sample pathwith source light returned from a reference reflector in the referencepath to create a wavelength dependent interferogram directed along adetection path to a detection module; wherein the video imaging pathcomprises: an illumination path including a source of optical radiationfor illuminating the sample; an image capture path including an imagecapture device for capturing an image of an illuminated region of thesubject; a beam combiner for coupling the illumination path with theimage capture path; a dichroic beamsplitter configured to couple thescanning beam OCT imaging path and the video imaging path, wherein thescanning beam OCT imaging path and the video imaging path share a commonobjective lens; and a fiber ring illuminator, wherein a ring ofillumination for the fiber ring illuminator is coaxial with the scanningbeam OCT imaging path over a region where the scanning beam OCT imagingpath and the video imaging path are in common; and wherein the fiberring illuminator comprises a ring of optical fibers that defines anannulus.
 2. The system of claim 1, wherein a radiant numerical apertureof the optical fibers in the annulus is between 0.16 and 0.28.
 3. Thesystem of claim 2: wherein the system further comprises a lens followingthe fiber ring illuminator and preceding the beam combiner that couplesthe illumination path with the image capture path; and wherein an imageof the ring illuminator is focused onto a vicinity of a pupil of an eyeof the subject.
 4. The system of claim 1, wherein the illumination pathfurther comprises a fixation target.
 5. The system of claim 4, whereinthe fixation target comprises one or more optical fibers situated withinan annular boundary of the ring illuminator, wherein end faces ofoptical fibers that comprise the fixation target are axially offset fromend faces of the optical fibers that comprise the ring illuminator. 6.The system of claim 1, wherein the image device is configured to:provide a real-time video image to aid alignment of an OCT beam; capturea photographic reference image of a sample to use as a comparison to anOCT depth-resolved image; enable full color or hyperspectral photographyfor emphasizing various features of an imaged structure and variousdepths of the image structure; and/or enable fluorescent imagephotography for emphasizing various features of the imaged structure andvarious depths of the image structure.
 7. The system of claim 1, whereinthe illumination source includes-optical radiation in a wavelength rangeof 650 to 740 nm.
 8. The system of claim 7, wherein the illuminationsource comprises a light emitting diode (LED).
 9. The system of claim 1,wherein the dichroic beamsplitter comprises a thin film filter.
 10. Thesystem of claim 1, wherein the system further includes a real-time rangefinder configured to guide a photographer to a correct working distancebetween the objective lens and the subject.
 11. The system of claim 1,further comprising an electromechanical reference arm.
 12. The system ofclaim 1, wherein the system is fitted within a compact housing, thehousing including a cable tether to a remainder of the OCT system, thehousing sized to provide a handheld system for imaging the subject.